The invention is related to large diameter heater rollers and specifically to the gudgeons and insulating sleeves that are parts of the heated roller assembly.
In the printing industries, heated rollers are commonly used to feed paper and also for electrostatographical machines serve as a fuser roller to fuse toner onto paper. The toner may be black or multicolor for color printing and copying. In such applications, as fuser rollers, the roller is supposted by gudgeons, also referred to as end caps, which are inserted into bearings, and the roller is typically rotated by a drive source connected to one of the gudgeons. The fusing of the toner requires typical temperatures of 300 to 400 degrees F. Fusing of the toner requires high pressure and therefore the fuser roller is engaged with another roller, typically called a pressure roller. When the two rollers are engaged, the elastomers on both rollers are compressed and the width of the compressed zone is generally known as nip width. In certain applications where image quality and high throughput are critical, large diameter fuser rollers are required. Large diameter fuser rollers are in excess of 4 inches in diameter and range from four to ten inch diameter, with a typical diameter of 6.4 inches. For precise controlling of the fusing temperature, heat loss through the gudgeons must be effectively minimized, through the proper material selection, bearing insulating sleeves and roller design.
Typically, metal gudgeons in conjunction with plastic insulating sleeves are used in fuser roller construction. The preferred gudgeon material is powder metal ( U.S. Pat. No. 5,094,613) due to lower thermal conductivity and near net shape manufacturing capability. The material selection is stainless steel (type 303, 304 or 316 stainless steel) although mild steel may also be used. The preferred method to assemble gudgeons to the core is by friction welding, due to the fact that the joint is permanent, capable of achieving tight tolerances and the process is extremely reliable. Other methods can be used such as press fits and bolt on designs which tend to be more costly and tend to be not as reliable. With large diameter fuser rollers, the length of the outside gudgeon diameter must be extended so that there is enough engagement for friction welding. The outside gudgeon diameter is required for engagement for friction welding due to the fact that extreme forces are generated during welding. If the small diameter was engaged, the gudgeon would fracture as a result of the welding process. As a result, in the manufacture of large diameter fuser rollers, the gudgeons are extremely expensive due to the excess material required for engagement for friction welding. In addition, machining this welded fuser roll assembly is costly due to extensive machining required due to the extra material.
A patent and literature search uncovered a Research Disclosure (No. 33279, Dec. 1991, see Attachment A), where in a heated roller (with possibly a large fusing diameter) having an extrusion profile of concentric circles connected with spokes. The gudgeons would be welded to the inner circle of the core resulting in reduced cost due to the reduced size of the gudgeon. The major problem with this design concept is that heat transfer through the spokes is inefficient and would not be suitable for a high output printer or copier. What is needed in the art is a low cost design for large diameter fuser rollers where thermal transfer through the gudgeons and the bearings are minimized.
The object of the present invention is to provide a heated roller, such as in a electrostatographic reproduction apparatus, which has a low design cost, which is suitable for large diameter fuser rollers, and in which thermal transfer through the gudgeons and the bearing are minimized. The gudgeon of the invention has slots, holes or similar configurations that serve for engagement during the friction welding process. The result is a significant reduction in unit manufacturing cost for the fuser roll assembly. In addition, the insulator sleeve is designed to fit between the gudgeon bearing diameter and the inside diameter of the bearing. The sleeve is designed so that there is engagement with the slots in the gudgeon so that the sleeve does not rotate when assembled to the fuser roller.